Field of the Invention
The present invention relates to a zoom lens which is suitable for an image pickup optical system that is used for an image pickup apparatus, for instance, such as a video camera, a monitoring camera, a digital still camera and a broadcasting camera.
Description of the Related Art
An image pickup optical system which is used for an image pickup apparatus that uses an image pickup element is required to be a zoom lens which has a high optical performance and such a wide angle of field as to facilitate wide area photographing. In a zoom lens to be mounted, for instance, on a monitoring camera, it is required that the whole system is miniaturized, and it is required to be such a zoom lens having a super-wide angle of field that the one camera can monitor a wide area range.
In addition, as for a viewpoint that the monitoring camera tends to show a higher image quality, in recent years, the zoom lens is required to correspond to a full HD (High Definition) image quality and 4K from an SD (Standard Definition) image quality, and is desired to have high resolution. Furthermore, as for a viewpoint of luminosity, the zoom lens has a small F number so as to adequately pick up an image in the time of twilight when the quantity of light decreases or in the night.
Japanese Patent Application Laid-Open No. 2012-22109 discloses a negative-lead type zoom lens which includes a first lens unit having a negative refractive power and a second lens unit having a positive refractive power, in order from an object side to an image side, and moves both of the lens units to perform zooming. The zoom lens of Japanese Patent Application Laid-Open No. 2012-22109 aims at satisfying both of the enhancement of the optical performance and the widening of the angle of field.
Here, it becomes important for the negative-lead type zoom lens to make a refractive power of each of the lens units, a lens configuration and the like appropriately set, in order to obtain a high optical performance over all zoom regions while the whole system is small and the angle of field is wide.